The work during the current year consisted of: (a) the isolation and characterization of a membrane-bound polysomal complex in ascites tumor cells, (b) the study of the biogenesis of polysomes in yeast cells and (c) the observation that there are no free nuclear particles that contain DNA-like RNA. These new observations consolidate our previous findings that mRNA does not appear as a ribonucleoprotein particle but is a component of a more complex structure which is tightly bound to the cytoplasmic membranes. With the discovery that even in the cell nucleus pre-mRNA and mRNA are components of a fibro-granular material which is also bound to the nuclear membrane, the hypothesis that the membranes play an important role in holding the mRNA molecules and are the site of polysomal formation is well supported. For the next year, the morphological aspects, chemical components and biochemical properties of the nuclear and cytoplasmic fibro-granular material that contains mRNA will be studied. In addition, the role of the newly synthesized ribosomal subunits as "specific activator" of the membrane-bound mRNA will be explored.